Description

Summary:
The bundled libfontconfig seems to cause problems when the target system uses
a newer font config format. See discussion here:

https://mail.kde.org/pipermail/kdevelop/2018-October/019726.html

It seems to be a common problem (as seen in bug reports of other AppImage
projects).

It's also blacklisted in linuxdeployqt:

https://github.com/AppImage/AppImages/blob/master/excludelist

For me locally, after the change I also have the exact same font appearance
as with native applications. Before the patch the fonts did use my
anti-aliasing settings iiuc. Before the patch, running the AppImage resulted
in lots of warnings: